Electrolyte and surface-active additives for the electrochemical deposition of smooth, dense aluminum layers from ionic liquids

ABSTRACT

The present invention relates to a process for the electrochemical deposition of aluminum, by means of which matt or shiny, dense aluminum layers can be obtained and which comprises the steps: (a) provision of an electrolysis apparatus having at least one anode and at least one cathode in an electrolysis space, (b) electrochemical deposition of aluminum on the at least one cathode of the electrolysis apparatus from an ionic liquid comprising anions and cations and also one or more metal salt(s) and one or more additive(s), wherein the current density at the at least one cathode is at least 50 A/m 2 .

The invention relates to a process for the electrochemical deposition of aluminum and also an electrolyte which can be used in this process.

Aluminum is an important material which is used predominantly in vehicle and aircraft construction and also in mechanical engineering, in building or construction and as packaging material. Electrolysis plays an important role both in the production of aluminum and in its purification.

The conventional process for the industrial production of aluminum is based on the Hall-Heroult process in which aluminum oxide in the form of bauxite is dissolved and aluminum is cathodically deposited by means of direct current from a melt at temperatures of about 1000° C. One process for the electrochemical deposition of aluminum is the SIGAL process in which a highly reactive, pyrophoric organoaluminum compound is handled in a flammable base electrolyte. Such organoaluminum compounds decompose spontaneously in air by reaction with atmospheric oxygen and moisture, resulting in flame formation. Such decomposition in the presence of readily flammable toluene or xylene electrolytes can lead to serious industrial accidents through to destruction of the plant.

Owing to the above-described disadvantages, efforts have been made to deposit aluminum from ionic liquids. The deposition of aluminum from ionic liquids has the advantage over the Sigal process that the electrolyte used is hard to ignite and although the aluminum precursor used is sensitive to hydrolysis, it is not pyrophoric.

A disadvantage of the use of electrolytes based on ionic liquids is the poor surface finish which is at present achieved at industrially relevant current densities of >200 A/m². Here, a poor surface finish is a rough, dendritic surface which does not cover the electrode or the substrate onto which it is deposited over the entire area. From decorative and corrosion protection points of view, an even deposit which is shiny or has a matt finish is desirable. A dense layer is indispensable for appropriate corrosion protection.

One document which is concerned with the deposition of metals from ionic liquids is DE 101 088 93. Here, mention is made of, for example, imidazole derivatives which when added to the ionic liquid influence the crystallite size of the deposited metal.

EP 0 084 816 discloses organometallic electrolytes for the electrochemical deposition of aluminum, which are said to have a high throwing power combined with good electrical conductivity.

Despite the processes known in the prior art, there is a need for alternative electrolysis processes for producing aluminum.

It is therefore an object of the present invention to provide an alternative electrolysis process for producing aluminum. A further object of the present invention is to provide a process for the electrochemical deposition of aluminum from ionic liquids by means of which matt or shiny dense aluminum layers can be obtained.

The object is achieved by a process for the electrochemical deposition of aluminum, which comprises the steps:

-   -   (a) provision of an electrolysis apparatus having at least one         anode and at least one cathode in an electrolysis space,     -   (b) electrochemical deposition of aluminum on the at least one         cathode of the electrolysis apparatus from an ionic liquid         comprising anions and cations and also one or more metal salt(s)         and one or more additive(s),         wherein the ionic liquid comprises from 0.1 to 10% by weight,         based on the total amount of the ionic liquid, of one or more         additive(s) selected from among one or more compound(s) of the         general formulae (I), (II) and (III) and the current density at         the at least one cathode is at least 50 A/m².

The additives of the general formulae (I), (II) and (III) are defined below:

The additive of the general formula (I) is a compound of the general formula (I),

where X¹ and X² are each, independently of one another, N or CH,

X³ is NR¹, O or S,

m is an integer from 0 to 4,

where at least two of X¹, X² and X³ are heteroatoms selected from among N, O and S, and

R¹ is selected from the group consisting of H, alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl and heterocyclyl, where the alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl and heterocyclyl groups are optionally substituted by one or more substituents and the alkyl and cycloalkyl groups are optionally interrupted by from 1 to 3 heteroatoms or functional groups, and

the radicals R² are each, independently of one another, H, alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl or heterocyclyl, where the alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl and heterocyclyl groups are optionally substituted by one or more substituents and the alkyl and cycloalkyl groups are optionally interrupted by from 1 to 3 heteroatoms or functional groups.

The additive of the general formula (II) is a compound of the general formula (II),

R³N⁺(R⁴)₃Hal⁻  (II)

where R³ is H, alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl or heterocyclyl, where the alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl and heterocyclyl groups are optionally substituted by one or more substituents and the alkyl and cycloalkyl groups are optionally interrupted by from 1 to 3 heteroatoms or functional groups, and

the radicals R⁴ are each, independently of one another, H, alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl or heterocyclyl, where the alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl and heterocyclyl groups are optionally substituted by one or more substituents and the alkyl and cycloalkyl groups are optionally interrupted by from 1 to 3 heteroatoms or functional groups, and Hal is selected from the group consisting of fluorine, chlorine, bromine and iodine.

The additive of the general formula (III) is a compound of the general formula (III),

R⁵SO₃ ⁻M⁺  (III)

where R⁵ is alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl or heterocyclyl, where the alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl and heterocyclyl groups are optionally substituted by one or more substituents and the alkyl and cycloalkyl groups are optionally interrupted by from 1 to 3 heteroatoms or by functional groups, and M⁺ is Na⁺ or K⁺.

The substituents are selected independently from the group consisting of fluorine, chlorine, bromine, iodine, optionally substituted alkyl, optionally substituted aryl, optionally substituted heterocyclyl, optionally substituted aralkyl, alkoxy, nitro, carboalkoxy, cyano, alkylmercaptyl, trihaloalkyl, carboxyalkyl, —(C₁-C₇)-alkyl, —O—(C₁-C₇)-alkyl, —N((C₁-C₄)-alkyl)₂, —CO—N((C₁-C₄)-alkyl)₂.

“Alkyl” is a saturated aliphatic hydrocarbon group which may be linear or branched and can have from 1 to 20 carbon atoms in the chain. Preferred alkyl groups can be linear or branched and have from 1 to 10 carbon atoms in the chain. Branched means that a lower alkyl group such as methyl, ethyl or propyl is attached to a linear alkyl chain. Alkyl is, for example, methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl, 2-methyl-1-propyl (isobutyl), 2-methyl-2-propyl (tert-butyl), 1-pentyl, 2-pentyl, 3-pentyl, 2-methyl-1-butyl, 3-methyl-1-butyl, 2-methyl-2-butyl, 3-methyl-2-butyl, 2,2-dimethyl-1-propyl, 1-hexyl, 2-hexyl, 3-hexyl, 2-methyl-1-pentyl, 3-methyl-1-pentyl, 4-methyl-1-pentyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl, 4-methyl-2-pentyl, 2-methyl-3-pentyl, 3-methyl-3-pentyl, 2,2-dimethyl-1-butyl, 2,3-dimethyl-1-butyl, 3,3-dimethyl-1-butyl, 2-ethyl-1-butyl, 2,3-dimethyl-2-butyl, 3,3-dimethyl-2-butyl, 1-heptyl, 1-octyl, 1-nonyl, 1-decyl, 1-undecyl, 1-dodecyl, 1-tetradecyl, 1-hexadecyl and 1-octadecyl.

“Substituted alkyl” means that the alkyl group is substituted by one or more substituents selected from among alkyl, optionally substituted aryl, optionally substituted aralkyl, alkoxy, nitro, carboalkoxy, cyano, halo, alkylmercaptyl, trihaloalkyl and carboxyalkyl.

“Cycloalkyl” is an aliphatic ring which has from 3 to above 10 carbon atoms in the ring. Preferred cycloalkyl groups have from 4 to about 7 carbon atoms in the ring.

“Aryl” is phenyl or naphthyl. “Aralkyl” is an alkyl group which is substituted by an aryl radical. “Substituted aralkyl” and “substituted aryl” means that the aryl group or the aryl group of the aralkyl group is substituted by one or more substituents selected from among alkyl, alkoxy, nitro, carboalkoxy, cyano, halo, alkylmercaptyl, trihaloalkyl and carboxyalkyl.

“Alkoxy” is an alkyl-O group in which “alkyl” is as defined above. Lower alkoxy groups are preferred. Examples of groups include methoxy, ethoxy, n-propoxy, i-propoxy and n-butoxy.

“Lower alkyl” is an alkyl group having from 1 to about 7 carbon atoms.

“Alkoxyalkyl” is an alkyl group as described above which is substituted by an alkoxy groups as described above.

“Halogen” (or “halo”) is chlorine (chloro), fluorine (fluoro), bromine (bromo) or iodine (iodo).

“Heterocyclyl” is an about 4- to about 10-membered ring structure in which one or more of the ring atoms is an element other than carbon, for example N, O or S. Heterocyclyl can be aromatic or nonaromatic, i.e. it can be saturated, partially unsaturated or fully unsaturated.

“Substituted heterocyclyl” means that the heterocyclyl group is substituted by one or more substituents, with substituents including: alkoxy, aryl, carboalkoxy, cyano, halo, heterocyclyl, trihalomethyl, alkylmercaptyl and nitro.

“Alkoxycarbonyl” is an alkoxy-C═O group.

“Aralkoxycarbonyl” is an aralkyl-O—C═O group.

“Aryloxycarbonyl” is an aryl-O—C═O group.

“Carboalkoxy” is a carboxyl substituent esterified by an alcohol of the formula C_(n)H_(2n+1)OH, where n is from 1 to about 6.

“Alkoxyalkyl” is an alkyl group as described above which is substituted by an alkoxy group as described above.

Possible heteroatoms in the definition of the radicals R¹, R², R³ and R⁴ are in principle all heteroatoms which are able to formally replace a —CH₂—, —CH═, —C≡ or ═C═ group. If the radical comprises heteroatoms, preference is given to oxygen, nitrogen, sulfur, phosphorus and silicon. As preferred groups, mention may be made of, in particular, —O—, —S—, —SO—, —SO₂—, —NR′—, —N═, —PR′—, —PR′₂ and —SiR′₂—, where the radicals R′ are in each case the remaining part of the radical.

Possible functional groups are in principle all functional groups which can be bound to a carbon atom or a heteroatom. Suitable examples are ═O (in particular as carbonyl group) and —CN (cyano). Functional groups and heteroatoms can also be directly adjacent, so that combinations of a plurality of adjacent atoms such as —O— (ether), —S— (thioether), —COO— (ester) or —CONR′— (tertiary amide) are also comprised, for example di(C₁-C₄-alkyl)amino, C₁-C₄-alkyloxycarbonyl or C₁-C₄-alkoxy.

In a preferred embodiment of the invention, R¹ is selected from among methyl, ethyl, 1-propyl, 1-butyl, 1-pentyl and 1-hexyl. In a particularly preferred embodiment of the invention, the radical R¹ is methyl.

In a preferred embodiment, R² is H and m is 4.

In a preferred embodiment of the invention, the compound of the general formula (I) is N-methylbenzotriazole.

In a particularly preferred embodiment of the invention, the compound of the general formula (I) is one or more compound(s) selected from among N-methylbenzodiazole, N-ethylbenzodiazole, benzoxazole, benzisooxazole, benzisothiazole and benzothiazole.

In a preferred embodiment of the invention, R³ is a linear, saturated aliphatic hydrocarbon group having from 5 to 20 carbon atoms in the chain, particularly preferably from 10 to 18 carbon atoms in the chain. In a preferred embodiment of the invention, the radicals R⁴ are identical or different and are selected from among H, methyl, ethyl, 1-propyl and 2-propyl.

In a particularly preferred embodiment of the invention, the compound of the general formula (II) is one or more compounds(s) selected from among hexadecyltrimethylammonium bromide and hexadecyltrimethylammonium chloride.

In a preferred embodiment of the invention, R⁵ is a linear, saturated aliphatic hydrocarbon group having from 5 to 20 carbon atoms in the chain, particularly preferably from 10 to 15 carbon atoms in the chain. In a particularly preferred embodiment of the invention, the compound of the general formula (III) is sodium lauryl sulfate.

The current density at which the process of the invention is carried out is at least 50 A/m², and can vary within a wide range. The electric current density is for the present purposes defined as the ratio of current to effective electrode area in the electrolysis. The electric current density is preferably at least 100 A/m², more preferably at least 200 A/m² and in particular at least 400 A/m²

It has been found that the use of one or more of the additives of the general formulae (I), (II) and (III) in the process of the invention carried out at current densities of at least 50 A/m² enables matt or shiny, dense aluminum layers to be obtained.

Ionic liquids are suitable electrolytes for the deposition of aluminum. The electrolytes are typically salt melts having a water content of less than 0.1% by weight, based on the total amount of the electrolyte.

In a general embodiment of the invention, the anion of the ionic liquid is tetrachloroaluminate.

As cations, preference is given to using dialkylimidazolium cations in which the two alkyl groups can be identical or different, branched or unbranched, unsubstituted or substituted by one or more phenyl groups and have from 1 to 6 carbon atoms.

Preference is given to benzylmethylimidazolium, hexylmethylimidazolium, butylmethylimidazolium, ethylmethylimidazolium. The ionic liquid very particularly preferably has a formula KaCl×n AlCl₃, where Ka is one of the abovementioned imidazolium cations and n is from 1.4 to 2.0, more preferably 1.4 to 1.7, in particular 1.5.

However, it is also possible to use further ionic liquids. Such ionic liquids are described, for example, in DE-A 10 2005 017 733.

Generally, preference is given here to ionic liquids which have cations selected from among the compounds of the formulae (IVa) to (IVw):

and oligomers comprising these structures.

Further suitable cations are compounds of the general formulae (IVx) and (IVy)

and oligomers comprising these structures.

In the abovementioned formulae (IVa) to (IVy)

-   -   the radical R is hydrogen, a carbon-comprising organic,         saturated or unsaturated, acyclic or cyclic, aliphatic, aromatic         or araliphatic radical which has from 1 to 20 carbon atoms and         is unsubstituted or interrupted or substituted by from 1 to 5         heteroatoms or functional groups; and     -   the radicals R¹ to R⁹ are each, independently of one another,         hydrogen, a sulfo group or a carbon-comprising organic,         saturated or unsaturated, acyclic or cyclic, aliphatic, aromatic         or araliphatic radical which has from 1 to 20 carbon atoms and         is unsubstituted or interrupted or substituted by from 1 to 5         heteroatoms or functional groups, where the radicals R¹ to R⁹         which in the abovementioned formulae (IV) are bound to a carbon         atom (and not to a heteroatom) may also be halogen or a         functional group; or     -   two adjacent radicals from among R¹ to R⁹ may together also form         a divalent, carbon-comprising organic, saturated or unsaturated,         acyclic or cyclic, aliphatic, aromatic or araliphatic radical         which has from 1 to 30 carbon atoms and is unsubstituted or         interrupted or substituted by from 1 to 5 heteroatoms or         functional groups.

In the definition of the radicals R and R¹ to R⁹, possible heteroatoms are in principle all heteroatoms which are able formally to replace a —CH₂— group, a —CH═ group, a —C≡ group or a ═C═ group. If the carbon-comprising radical comprises heteroatoms, preference is given to oxygen, nitrogen, sulfur, phosphorus and silicon. Preferred groups are, in particular, —O—, —S—, —SO—, —SO₂—, —NR′—, —N═, —PR′—, —PR′₂ and —SiR′₂—, where the radicals R′ are the remaining part of the carbon-comprising radical. In cases in which the radicals R¹ to R⁹ in the abovementioned formulae (IV) are bound to a carbon atom and (not to a heteroatom), these can also be bound directly via the heteroatom.

Possible functional groups are in principle all functional groups which can be bound to a carbon atom or a heteroatom. Examples of suitable functional groups are ═O (in particular as carbonyl group) and —CN (cyano). Functional groups and heteroatoms can also be directly adjacent, so that combinations of a plurality of adjacent atoms such as —O— (ether), —S— (thioether), —COO— (ester) or —CONR′— (tertiary amide) are also comprised, for example di(C₁-C₄-alkyl)amino, C₁-C₄-alkyloxycarbonyl or C₁-C₄-alkyloxy.

As halogens, mention may be made of fluorine, chlorine, bromine and iodine.

The radical R is preferably

-   -   unbranched or branched C₁-C₁₈-alkyl which has a total of from 1         to 20 carbon atoms is unsubstituted or substituted by one or         more halogen, phenyl, cyano, C₁-C₆-alkoxycarbonyl groups, for         example methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl,         2-methyl-1-propyl (isobutyl), 2-methyl-2-propyl (tert-butyl),         1-pentyl, 2-pentyl, 3-pentyl, 2-methyl-1-butyl,         3-methyl-1-butyl, 2-methyl-2-butyl, 3-methyl-2-butyl,         2,2-dimethyl-1-propyl, 1-hexyl, 2-hexyl, 3-hexyl,         2-methyl-1-pentyl, 3-methyl-1-pentyl, 4-methyl-1-pentyl,         2-methyl-2-pentyl, 3-methyl-2-pentyl, 4-methyl-2-pentyl,         2-methyl-3-pentyl, 3-methyl-3-pentyl, 2,2-dimethyl-1-butyl,         2,3-dimethyl-1-butyl, 3,3-dimethyl-1-butyl, 2-ethyl-1-butyl,         2,3-dimethyl-2-butyl, 3,3-dimethyl-2-butyl, 1-heptyl, 1-octyl,         1-nonyl, 1-decyl, 1-undecyl, 1-dodecyl, 1-tetradecyl,         1-hexadecyl, 1-octadecyl, benzyl, 3-phenylpropyl, 2-cyanoethyl,         2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl,         2-(n-butoxycarbonyl)ethyl, trifluoromethyl, difluoromethyl,         fluoromethyl, pentafluoroethyl, heptafluoropropyl,         heptafluoroisopropyl, nonafluorobutyl, nonafluoroisobutyl,         undecylfluoropentyl, undecylfluoroisopentyl;     -   glycols, butylene glycols and their oligomers having from 1 to         100 units and a hydrogen or a C₁-C₈-alkyl as end group, for         example R^(A)O—(CHR^(B)—CH₂—O)_(n)—CHR^(B)—CH₂— or         R^(A)O—(CH₂CH₂CH₂CH₂O)_(n)—CH₂CH₂CH₂CH₂O— where R^(B) are each         preferably hydrogen, methyl or ethyl and n is preferably from 0         to 3, in particular 3-oxabutyl, 3-oxapentyl, 3,6-dioxaheptyl,         3,6-dioxaoctyl, 3,6,9-trioxadecyl, 3,6,9-trioxaundecyl,         3,6,9,12-tetraoxatridecyl and 3,6,9,12-tetraoxatetradecyl;     -   vinyl; and         -   N,N-di-C₁-C₆-alkylamino, for example N,N-dimethylamino and             N,N-diethylamino.

The radical R is particularly preferably unbranched and unsubstituted C₁-C₁₈-alkyl, for example methyl, ethyl, 1-propyl, 1-butyl, 1-pentyl, 1-hexyl, 1-heptyl, 1-octyl, 1-decyl, 1-dodecyl, 1-tetradecyl, 1-hexadecyl, 1-octadecyl, in particular methyl, ethyl, 1-butyl and 1-octyl, or CH₃O—(CH₂CH₂O)_(n)—CH₂CH₂— and CH₃CH₂O—(CH₂CH₂O)_(n)—CH₂CH₂— where n is from 0 to 3.

Preference is given to the radicals R¹ to R⁹ each being, independently of one another,

-   -   hydrogen;     -   halogen;     -   a functional group;     -   C₁-C₁₈-alkyl which is optionally substituted by functional         groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms         and/or heterocycles and/or interrupted by one or more oxygen         and/or sulfur atoms and/or one or more substituted or         unsubstituted imino groups;     -   C₂-C₁₈-alkenyl which is optionally substituted by functional         groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms         and/or heterocycles and/or interrupted by one or more oxygen         and/or sulfur atoms and/or one or more substituted or         unsubstituted imino groups;     -   C₆-C₁₂-aryl which is optionally substituted by functional         groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms         and/or heterocycles;     -   C₅-C₁₂-cycloalkyl which is optionally substituted by functional         groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms         and/or heterocycles;     -   C₅-C₁₂-cycloalkenyl which is optionally substituted by         functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen,         heteroatoms and/or heterocycles; or     -   a five- or six-membered, oxygen-, nitrogen- and/or         sulfur-comprising heterocycle which is optionally substituted by         functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen,         heteroatoms and/or heterocycles; or         two adjacent radicals together form     -   an unsaturated, saturated or aromatic ring which is optionally         substituted by functional groups, aryl, alkyl, aryloxy,         alkyloxy, halogen, heteroatoms and/or heterocycles and is         optionally interrupted by one or more oxygen and/or sulfur atoms         and/or one or more substituted or unsubstituted imino groups.

C₁-C₁₈-Alkyl which is optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles is preferably methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl, 2-methyl-1-propyl (isobutyl), 2-methyl-2-propyl (tert-butyl), 1-pentyl, 2-pentyl, 3-pentyl, 2-methyl-1-butyl, 3-methyl-1-butyl, 2-methyl-2-butyl, 3-methyl-2-butyl, 2,2-dimethyl-1-propyl, 1-hexyl, 2-hexyl, 3-hexyl, 2-methyl-1-pentyl, 3-methyl-1-pentyl, 4-methyl-1-pentyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl, 4-methyl-2-pentyl, 2-methyl-3-pentyl, 3-methyl-3-pentyl, 2,2-dimethyl-1-butyl, 2,3-dimethyl-1-butyl, 3,3-dimethyl-1-butyl, 2-ethyl-1-butyl, 2,3-dimethyl-2-butyl, 3,3-dimethyl-2-butyl, heptyl, octyl, 2-ethylhexyl, 2,4,4-trimethylpentyl, 1,1,3,3-tetramethylbutyl, 1-nonyl, 1-decyl, 1-undecyl, 1-dodecyl, 1-tridecyl, 1-tetradecyl, 1-pentadecyl, 1-hexadecyl, 1-heptadecyl, 1-octadecyl, cyclopentylmethyl, 2-cyclopentylethyl, 3-cyclopentylpropyl, cyclohexylmethyl, 2-cyclohexylethyl, 3-cyclohexylpropyl, benzyl (phenylmethyl), diphenylmethyl (benzhydryl), triphenylmethyl, 1-phenylethyl, 2-phenylethyl, 3-phenylpropyl, a,a-dimethylbenzyl, p-tolylmethyl, 1-(p-butylphenyl)ethyl, p-chlorobenzyl, 2,4-dichlorobenzyl, p-methoxybenzyl, m-ethoxybenzyl, 2-cyanoethyl, 2-cyanopropyl, 2-methoxycarbonylethyl, 2-ethoxycarbonylethyl, 2-butoxycarbonyl-propyl, 1,2-di(methoxycarbonyl)ethyl, methoxy, ethoxy, 1,3-dioxolan-2-yl, 1,3-dioxan-2-yl, 2-methyl-1,3-dioxolan-2-yl, 4-methyl-1,3-dioxolan-2-yl, 2-dimethylaminoethyl, 2-dimethylaminopropyl, 3-dimethylaminopropyl, 4-dimethylaminobutyl, 6-dimethylaminohexyl, 2-phenoxyethyl, 2-phenoxypropyl, 3-phenoxypropyl, 4-phenoxybutyl, 6-phenoxyhexyl, 2-methoxyethyl, 2-methoxypropyl, 3-methoxypropyl, 4-methoxybutyl, 6-methoxyhexyl, 2-ethoxyethyl, 2-ethoxypropyl, 3-ethoxypropyl, 4-ethoxybutyl, 6-ethoxyhexyl, acetyl, C_(n)F_(2(n−a)+(1−b))H_(2a+b) where n is from 1 to 30, 0≦a≦n and b=0 or 1 (for example CF₃, C₂F₅, CH₂CH₂—C_((n−2))F_(2(n−2)+1), C₆F₁₃, C₈F₁₇, C₁₀F₂₁, C₁₂F₂₅), chloromethyl, 2-chloroethyl, trichloromethyl, 1,1-dimethyl-2-chloroethyl, methoxymethyl, 2-butoxyethyl, diethoxymethyl, diethoxyethyl, 2-isopropoxyethyl, 2-butoxypropyl, 2-octyloxyethyl, 2-methoxyisopropyl, 2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl, 2-(n-butoxycarbonyl)ethyl, butylthiomethyl, 2-dodecylthioethyl, 2-phenylthioethyl, 5-methoxy-3-oxapentyl, 8-methoxy-3,6-dioxaoctyl, 11-methoxy-3,6,9-trioxaundecyl, 7-methoxy-4-oxaheptyl, 11-methoxy-4,8-dioxaundecyl, 15-methoxy-4,8,12-trioxapentadecyl, 9-methoxy-5-oxanonyl, 14-methoxy-5,10-dioxatetradecyl, 5-ethoxy-3-oxapentyl, 8-ethoxy-3,6-dioxaoctyl, 11-ethoxy-3,6,9-trioxaundecyl, 7-ethoxy-4-oxaheptyl, 11-ethoxy-4,8-dioxaundecyl, 15-ethoxy-4,8,12-trioxapentadecyl, 9-ethoxy-5-oxanonyl or 14-ethoxy-5,10-oxatetradecyl.

C₂-C₁₈-Alkenyl which is optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles and/or interrupted by one or more oxygen and/or sulfur atoms and/or one or more substituted or unsubstituted imino groups is preferably vinyl, 2-propenyl, 3-butenyl, cis-2-butenyl, trans-2-butenyl or C_(n)F_(2(n−a)−(1−b))H_(2a−b) where n≦30, 0≦a≦n and b=0 or 1.

C₆-C₁₂-Aryl which is optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles is preferably phenyl, tolyl, xylyl, α-naphthyl, β-naphthyl, 4-diphenylyl, chlorophenyl, dichlorophenyl, trichlorophenyl, difluorophenyl, methylphenyl, dimethylphenyl, trimethylphenyl, ethylphenyl, diethylphenyl, isopropylphenyl, tert-butylphenyl, dodecylphenyl, methoxyphenyl, dimethoxyphenyl, ethoxyphenyl, hexyloxyphenyl, methylnaphthyl, isopropylnaphthyl, chloronaphthyl, ethoxynaphthyl, 2,6-dimethylphenyl, 2,4,6-trimethylphenyl, 2,6-dimethoxyphenyl, 2,6-dichlorophenyl, 4-bromophenyl, 2-nitrophenyl, 4-nitrophenyl, 2,4-dinitrophenyl, 2,6-dinitrophenyl, 4-dimethylaminophenyl, 4-acetylphenyl, methoxyethylphenyl, ethoxymethylphenyl, methylthiophenyl, isopropylthiophenyl or tert-butylthiophenyl or C₆F_((5−a))H_(a) where 0≦a≦5.

C₅-C₁₂-Cycloalkyl which is optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles is preferably cyclopentyl, cyclohexyl, cyclooctyl, cyclododecyl, methylcyclopentyl, dimethylcyclopentyl, methyl-cyclohexyl, dimethylcyclohexyl, diethylcyclohexyl, butylcyclohexyl, methoxycyclohexyl, dimethoxycyclohexyl, diethoxycyclohexyl, butylthiocyclohexyl, chlorocyclohexyl, dichlorocyclohexyl, dichlorocyclopentyl, C_(n)F_(2(n−a)−(1−b))H_(2a−b) where n≦30, 0≦a≦n and b=0 or 1 or a saturated or unsaturated bicyclic system such as norbornyl or norbornenyl.

C₅-C₁₂-Cycloalkenyl which is optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles is preferably 3-cyclopentenyl, 2-cyclohexenyl, 3-cyclohexenyl, 2,5-cyclohexadienyl or C_(n)F_(2(n−a)−3(1−b))H_(2a−3b) where n≦30, 0≦a≦n and b=0 or 1.

A five- or six-membered, oxygen-, nitrogen- and/or sulfur-comprising heterocycle which is optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles is preferably furyl, thiophenyl, pyrryl, pyridyl, indolyl, benzoxazolyl, dioxolyl, dioxyl, benzimidazolyl, benzthiazolyl, dimethylpyridyl, methylquinolyl, dimethylpyrryl, methoxyfuryl, dimethoxypyridyl or difluoropyridyl.

If two adjacent radicals together form an unsaturated, saturated or aromatic ring which is optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles and may optionally be interrupted by one or more oxygen and/or sulfur atoms and/or one or more substituted or unsubstituted imino groups, the two radicals together are preferably 1,3-propylene, 1,4-butylene, 1,5-pentylene, 2-oxa-1,3-propylene, 1-oxa-1,3-propylene, 2-oxa-1,3-propylene, 1-oxa-1,3-propenylene, 3-oxa-1,5-pentylene, 1-aza-1,3-propenylene, 1-C₁-C₄-alkyl-1-aza-1,3-propenylene, 1,4-buta-1,3-dienylene, 1-aza-1,4-buta-1,3-dienylene or 2-aza-1,4-buta-1,3-dienylene.

If the abovementioned radicals comprise oxygen and/or sulfur atoms and/or substituted or unsubstituted imino groups, the number of oxygen and/or sulfur atoms and/or imino groups is not subject to any restrictions. There will generally be no more than 5 in the radical, preferably no more than 4 and very particularly preferably no more than 3.

If the abovementioned radicals comprise heteroatoms, there will generally be at least one carbon atom, preferably at least two carbon atoms, between each two heteroatoms.

Particular preference is given to the radicals R¹ to R⁹ each being, independently of one another,

-   -   hydrogen;     -   unbranched or branched C₁-C₁₈-alkyl which has a total of from 1         to 20 carbon atoms and is unsubstituted or substituted by one or         more hydroxy, halogen, phenyl, cyano, C₁-C₆-alkoxycarbonyl         and/or sulfonic acid groups, for example methyl, ethyl,         1-propyl, 2-propyl, 1-butyl, 2-butyl, 2-methyl-1-propyl         (isobutyl), 2-methyl-2-propyl (tert-butyl), 1-pentyl, 2-pentyl,         3-pentyl, 2-methyl-1-butyl, 3-methyl-1-butyl, 2-methyl-2-butyl,         3-methyl-2-butyl, 2,2-dimethyl-1-propyl, 1-hexyl, 2-hexyl,         3-hexyl, 2-methyl-1-pentyl, 3-methyl-1-pentyl,         4-methyl-1-pentyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl,         4-methyl-2-pentyl, 2-methyl-3-pentyl, 3-methyl-3-pentyl,         2,2-dimethyl-1-butyl, 2,3-dimethyl-1-butyl,         3,3-dimethyl-1-butyl, 2-ethyl-1-butyl, 2,3-dimethyl-2-butyl,         3,3-dimethyl-2-butyl, 1-heptyl, 1-octyl, 1-nonyl, 1-decyl,         1-undecyl, 1-dodecyl, 1-tetradecyl, 1-hexadecyl, 1-octadecyl,         benzyl, 3-phenylpropyl, 2-cyanoethyl, 2-(methoxycarbonyl)ethyl,         2-(ethoxycarbonyl)ethyl, 2-(n-butoxycarbonyl)ethyl,         trifluoromethyl, difluoromethyl, fluoromethyl, pentafluoroethyl,         heptafluoropropyl, heptafluoroisopropyl, nonafluorobutyl,         nonafluoroisobutyl, undecylfluoropentyl, undecylfluoroisopentyl;     -   glycols, butylene glycols and their oligomers having from 1 to         100 units and a hydrogen or a C₁-C₈-alkyl as end group, for         example R^(A)O—(CHR^(B)—CH₂—O)_(n)—CHR^(B)—CH₂— or         R^(A)O—(CH₂CH₂CH₂CH₂O)_(n)—CH₂CH₂CH₂CH₂O— where R^(A) and R^(B)         are each preferably hydrogen, methyl or ethyl and n is         preferably from 0 to 3, in particular 3-oxabutyl, 3-oxapentyl,         3,6-dioxaheptyl, 3,6-dioxaoctyl, 3,6,9-trioxadecyl,         3,6,9-trioxaundecyl, 3,6,9,12-tetraoxatridecyl and         3,6,9,12-tetraoxatetradecyl;     -   vinyl; and     -   N,N-di-C₁-C₆-alkylamino, for example N,N-dimethylamino and         N,N-diethylamino.

Very particular preference is given to the radicals R¹ to R⁹ each being, independently of one another, hydrogen or C₁-C₁₈-alkyl, for example methyl, ethyl, 1-butyl, 1-pentyl, 1-hexyl, 1-heptyl, 1-octyl, phenyl, 2-cyanoethyl, 2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl, 2-(n-butoxycarbonyl)ethyl, N,N-dimethylamino, N,N-diethylamino, chlorine or CH₃O—(CH₂CH₂O)_(n)—CH₂CH₂— or CH₃CH₂O—(CH₂CH₂O)_(n)—CH₂CH₂— where n is from 0 to 3.

Very particularly preferred pyridinium ions (IVa) are those in which

-   -   one of the radicals R¹ to R⁵ is methyl, ethyl or chlorine and         the remaining radicals R¹ to R⁵ are each hydrogen;     -   R³ is dimethylamino and the remaining radicals R¹, R², R⁴ and R⁵         are each hydrogen;     -   all radicals R¹ to R⁵ are hydrogen;     -   R² is carboxy or carboxamide and the remaining radicals R¹, R²,         R⁴ and R⁵ are each hydrogen; or     -   R¹ and R² or R² and R³ are together 1,4-buta-1,3-dienylene and         the remaining radicals R¹, R², R⁴ and R⁵ are each hydrogen;         and in particular those in which     -   R¹ to R⁵ are each hydrogen; or     -   one of the radicals R¹ to R⁵ is methyl or ethyl and the         remaining radicals R¹ to R⁵ are each hydrogen.

As very particularly preferred pyridinium ions (IVa), mention may be made of 1-methylpyridinium, 1-ethylpyridinium, 1-(1-butyl)pyridinium, 1-(1-hexyl)pyridinium, 1-(1-octyl)pyridinium, 1-(1-hexyl)pyridinium, 1-(1-octyl)pyridinium, 1-(1-dodecyl)-pyridinium, 1-(1-tetradecyl)pyridinium, 1-(1-hexadecyl)pyridinium, 1,2-dimethyl-pyridinium, 1-ethyl-2-methylpyridinium, 1-(1-butyl)-2-methylpyridinium, 1-(1-hexyl)-2-methylpyridinium, 1-(1-octyl)-2-methylpyridinium, 1-(1-dodecyl)-2-methylpyridinium, 1-(1-tetradecyl)-2-methylpyridinium, 1-(1-hexadecyl)-2-methylpyridinium, 1-methyl-2-ethylpyridinium, 1,2-diethylpyridinium, 1-(1-butyl)-2-ethylpyridinium, 1-(1-hexyl)-2-ethylpyridinium, 1-(1-octyl)-2-ethylpyridinium, 1-(1-dodecyl)-2-ethylpyridinium, 1-(1-tetradecyl)-2-ethylpyridinium, 1-(1-hexadecyl)-2-ethylpyridinium, 1,2-dimethyl-5-ethylpyridinium, 1,5-diethyl-2-methylpyridinium, 1-(1-butyl)-2-methyl-3-ethyl-pyridinium, 1-(1-hexyl)-2-methyl-3-ethylpyridinium and 1-(1-octyl)-2-methyl-3-ethyl-pyridinium, 1-(1-dodecyl)-2-methyl-3-ethylpyridinium, 1-(1-tetradecyl)-2-methyl-3-ethyl-pyridinium and 1-(1-hexadecyl)-2-methyl-3-ethylpyridinium.

Very particularly preferred pyridazinium ions (IVb) are those in which

-   -   R¹ to R⁴ are each hydrogen; or     -   one of the radicals R¹ to R⁴ is methyl or ethyl and the         remaining radicals R¹ to R⁴ are each hydrogen.

Very particularly preferred pyrimidinium ions (IVc) are those in which

-   -   R¹ is hydrogen, methyl or ethyl and R² to R⁴ are each,         independently of one another, hydrogen or methyl; or     -   R¹ is hydrogen, methyl or ethyl, R² and R⁴ are each methyl and         R³ is hydrogen.

Very particularly preferred pyrazinium ions (IVd) are those in which

-   -   R¹ is hydrogen, methyl or ethyl and R² to R⁴ are each,         independently of one another, hydrogen or methyl;     -   R¹ is hydrogen, methyl or ethyl, R² and R⁴ are each methyl and         R³ is hydrogen;     -   R¹ to R⁴ are each methyl; or     -   R¹ to R⁴ are each hydrogen.

Very particularly preferred imidazolium ions (IVe) are those in which

-   -   R¹ is hydrogen, methyl, ethyl, 1-propyl, 1-butyl, 1-pentyl,         1-hexyl, 1-octyl, 2-hydroxyethyl or 2-cyanoethyl and R² to R⁴         are each, independently of one another, hydrogen, methyl or         ethyl.

As very particularly preferred imidazolium ions (IVe), mention may be made of 1,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium, 1-(1-butyl)-3-methylimidazolium, 1-(1-butyl)-3-ethylimidazolium, 1-(1-hexyl)-3-methylimidazolium, 1-(1-hexyl)-3-ethylimidazolium, 1-(1-hexyl)-3-butylimidazolium, 1-(1-octyl)-3-methylimidazolium, 1-(1-octyl)-3-ethylimidazolium, 1-(1-octyl)-3-butylimidazolium, 1-(1-dodecyl)-3-methylimidazolium, 1-(1-dodecyl)-3-ethylimidazolium, 1-(1-dodecyl)-3-butylimidazolium, 1-(1-dodecyl)-3-octylimidazolium, 1-(1-tetradecyl)-3-methylimidazolium, 1-(1-tetradecyl)-3-ethylimidazolium, 1-(1-tetradecyl)-3-butylimidazolium, 1-(1-tetradecyl)-3-octylimidazolium, 1-(1-hexadecyl)-3-methylimidazolium, 1-(1-hexadecyl)-3-ethyl-imidazolium, 1-(1-hexadecyl)-3-butylimidazolium, 1-(1-hexadecyl)-3-octylimidazolium, 1,2-dimethylimidazolium, 1,2,3-trimethylimidazolium, 1-ethyl-2,3-dimethylimidazolium, 1-(1-butyl)-2,3-dimethylimidazolium, 1-(1-hexyl)-2,3-dimethylimidazolium, 1-(1-octyl)-2,3-dimethylimidazolium, 1,4-dimethylimidazolium, 1,3,4-trimethylimidazolium, 1,4-dimethyl-3-ethylimidazolium, 3-butylimidazolium, 1,4-dimethyl-3-octylimidazolium, 1,4,5-trimethylimidazolium, 1,3,4,5-tetramethylimidazolium, 1,4,5-trimethyl-3-ethylimidazolium, 1,4,5-trimethyl-3-butylimidazolium and 1,4,5-trimethyl-3-octylimidazolium.

Very particularly preferred pyrazolium ions (IVf), (IVg) and (IVg′) are those in which

-   -   R¹ is hydrogen, methyl or ethyl and R² to R⁴ are each,         independently of one another, hydrogen or methyl.

Very particularly preferred pyrazolium ions (IVh) are those in which

-   -   R¹ to R⁴ are each, independently of one another, hydrogen or         methyl.

Very particularly preferred 1-pyrazolinium ions (IVi) are those in which

-   -   R¹ to R⁶ are each, independently of one another, hydrogen or         methyl.

Very particularly preferred 2-pyrazolinium ions (IVj) and (IVj′) are those in which

-   -   R¹ is hydrogen, methyl, ethyl or phenyl and R² to R⁶ are each,         independently of one another, hydrogen or methyl.

Very particularly preferred 3-pyrazolinium ions (IVk) and (IVk′) are those in which

-   -   R¹ and R² are each, independently of one another, hydrogen,         methyl, ethyl or phenyl and R³ to R⁶ are each, independently of         one another, hydrogen or methyl.

Very particularly preferred imidazolinium ions (IVI) are those in which

-   -   R¹ and R² are each, independently of one another, hydrogen,         methyl, ethyl, 1-butyl or phenyl, R³ and R⁴ are each,         independently of one another, hydrogen, methyl or ethyl and R⁵         and R⁶ are each, independently of one another, hydrogen or         methyl.

Very particularly preferred imidazolinium ions (IVm) and (IVm′) are those in which

-   -   R¹ and R² are each, independently of one another, hydrogen,         methyl or ethyl and R³ to R⁶ are each, independently of one         another, hydrogen or methyl.

Very particularly preferred imidazolinium ions (IVn) and (IVn′) are those in which

-   -   R¹ to R³ are each, independently of one another, hydrogen,         methyl or ethyl and R⁴ to R⁶ are each, independently of one         another, hydrogen or methyl.

Very particularly preferred thiazolium ions (IVo) and (IVo′) and oxazolium ions (IVp) are those in which

-   -   R¹ is hydrogen, methyl, ethyl or phenyl and R² and R³ are each,         independently of one another, hydrogen or methyl.

Very particularly preferred 1,2,4-triazolium ions (IVq), (IVq′) and (IVq″) are those in which

-   -   R¹ and R² are each, independently of one another, hydrogen,         methyl, ethyl or phenyl and R³ is hydrogen, methyl or phenyl.

Very particularly preferred 1,2,3-triazolium ions (IVr), (IVr′) and (IVr″) are those in which

-   -   R¹ is hydrogen, methyl or ethyl and R² and R³ are each,         independently of one another, hydrogen or methyl or R² and R³         together are 1,4-buta-1,3-dienylene.

Very particularly preferred pyrrolidinium ions (IVs) are those in which

-   -   R¹ is hydrogen, methyl, ethyl or phenyl and R² to R⁹ are each,         independently of one another, hydrogen or methyl.

Very particularly preferred imidazolidinium ions (IVt) are those in which

-   -   R¹ and R⁴ are each, independently of one another, hydrogen,         methyl, ethyl or phenyl and R² and R³ and also R⁵ to R⁸ are         each, independently of one another, hydrogen or methyl.

Very particularly preferred ammonium ions (IVu) are those in which

-   -   R¹ to R³ are each, independently of one another, C₁-C₁₈-alkyl;         or     -   R¹ and R² together are 1,5-pentylene or 3-oxa-1,5-pentylene and         R³ is C₁-C₁₈-alkyl or 2-cyanoethyl.

As very particularly preferred ammonium ions (IVu), mention may be made of methyltri-(1-butyl)ammonium, N,N-dimethylpiperidinium and N,N-dimethylmorpholinium.

Examples of tertiary amines from which the quaternary ammonium ions of the general formula (IVu) are derived by quaternization with the abovementioned radicals R are diethyl-n-butylamine, diethyl-tert-butylamine, diethyl-n-pentylamine, diethylhexylamine, diethyloctylamine, diethyl(2-ethylhexyl)amine, di-n-propylbutylamine, di-n-propyl-n-pentylamine, di-n-propylhexylamine, di-n-propyloctylamine, di-n-propyl(2-ethylhexyl)-amine, diisopropylethylamine, diisopropyl-n-propylamine, diisopropylbutylamine, diisopropylpentylamine, diisopropylhexylamine, diisopropyloctylamine, diisopropyl-(2-ethylhexyl)amine, di-n-butylethylamine, di-n-butyl-n-propylamine, di-n-butyl-n-pentylamine, di-n-butylhexylamine, di-n-butyloctylamine, di-n-butyl(2-ethylhexyl)-amine, N-n-butylpyrrolidine, N-sec-butylpyrrolidine, N-tert-butylpyrrolidine, N-n-pentyl-pyrrolidine, N,N-dimethylcyclohexylamine, N,N-diethylcyclohexylamine, N,N-di-n-butyl-cyclohexylamine, N-n-propylpiperidine, N-isopropylpiperidine, N-n-butylpiperidine, N-sec-butylpiperidine, N-tert-butylpiperidine, N-n-pentylpiperidine, N-n-butylmorpholine, N-sec-butylmorpholine, N-tert-butylmorpholine, N-n-pentylmorpholine, N-benzyl-N-ethylaniline, N-benzyl-N-n-propylaniline, N-benzyl-N-isopropylaniline, N-benzyl-N-n-butylaniline, N,N-dimethyl-p-toluidine, N,N-diethyl-p-toluidine, N,N-di-n-butyl-p-toluidine, diethylbenzylamine, di-n-propylbenzylamine, di-n-butylbenzylamine, diethylphenylamine, di-n-propylphenylamine and di-n-butylphenylamine.

Preferred tertiary amines (IVu) are diisopropylethylamine, diethyl-tert-butylamine, diiso-propylbutylamine, di-n-butyl-n-pentylamine, N,N-di-n-butylcyclohexylamine and tertiary amines derived from pentylisomers.

Very particularly preferred tertiary amines are di-n-butyl-n-pentylamine and tertiary amines derived from pentylisomers. A further preferred tertiary amine which has three identical radicals is triallylamine.

Very particularly preferred guanidinium ions (IVv) are those in which

-   -   R¹ to R⁵ are each methyl.

Very particularly preferred guanidinium ions (IVv), mention may be made of N,N,N′,N′,N″,N″-hexamethylguanidinium.

Very particularly preferred cholinium ions (IVw) are those in which

-   -   R¹ and R² are each, independently of one another, methyl, ethyl,         1-butyl or 1-octyl and R³ is hydrogen, methyl, ethyl, acetyl,         —SO₂OH or —PO(OH)₂;     -   R¹ is methyl, ethyl, 1-butyl or 1-octyl, R² is a —CH₂—CH₂—OR⁴         group and R³ and R⁴ are each, independently of one another,         hydrogen, methyl, ethyl, acetyl, —SO₂OH or —PO(OH)₂; or     -   R¹ is a —CH₂—CH₂—OR⁴ group, R² is a —CH₂—CH₂—OR⁵ group and R³ to         R⁵ are each, independently of one another, hydrogen, methyl,         ethyl, acetyl, —SO₂OH or —PO(OH)₂.

Particular preference is given to cholinium ions (IVw) in which R³ is selected from among hydrogen, methyl, ethyl, acetyl, 5-methoxy-3-oxapentyl, 8-methoxy-3,6-dioxa-octyl, 11-methoxy-3,6,9-trioxaundecyl, 7-methoxy-4-oxaheptyl, 11-methoxy-4,8-dioxa-undecyl, 15-methoxy-4,8,12-trioxapentadecyl, 9-methoxy-5-oxanonyl, 14-methoxy-5,10-oxatetradecyl, 5-ethoxy-3-oxapentyl, 8-ethoxy-3,6-dioxaoctyl, 11-ethoxy-3,6,9-trioxaundecyl, 7-ethoxy-4-oxaheptyl, 11-ethoxy-4,8-dioxaundecyl, 15-ethoxy-4,8,12-trioxapentadecyl, 9-ethoxy-5-oxanonyl or 14-ethoxy-5,10-oxatetradecyl.

Very particularly preferred phosphonium ions (IVx) are those in which

-   -   R¹ to R³ are each, independently of one another, C₁-C₁₈-alkyl,         in particular butyl, isobutyl, 1-hexyl or 1-octyl.

General preference is given to cations having one or more of the general formulae IVa, IVe, IVs and IVu.

Among the abovementioned heterocyclic cations, preference is given to the pyridinium ions, pyrazolinium ions, pyrazolium ions and the imidazolinium and imidazolium ions. Ammonium ions are also preferred.

Particular preference is given to 1-methylpyridinium, 1-ethylpyridinium, 1-(1-butyl)-pyridinium, 1-(1-hexyl)pyridinium, 1-(1-octyl)pyridinium, 1-(1-hexyl)pyridinium, 1-(1-octyl)pyridinium, 1-(1-dodecyl)pyridinium, 1-(1-tetradecyl)pyridinium, 1-(1-hexa-decyl)pyridinium, 1,2-dimethylpyridinium, 1-ethyl-2-methylpyridinium, 1-(1-butyl)-2-methylpyridinium, 1-(1-hexyl)-2-methylpyridinium, 1-(1-octyl)-2-methylpyridinium, 1-(1-dodecyl)-2-methylpyridinium, 1-(1-tetradecyl)-2-methylpyridinium, 1-(1-hexadecyl)-2-methylpyridinium, 1-methyl-2-ethylpyridinium, 1,2-diethylpyridinium, 1-(1-butyl)-2-ethylpyridinium, 1-(1-hexyl)-2-ethylpyridinium, 1-(1-octyl)-2-ethylpyridinium, 1-(1-dodecyl)-2-ethylpyridinium, 1-(1-tetradecyl)-2-ethylpyridinium , 1-(1-hexadecyl)-2-ethylpyridinium, 1,2-dimethyl-5-ethylpyridinium, 1,5-diethyl-2-methylpyridinium, 1-(1-butyl)-2-methyl-3-ethylpyridinium, 1-(1-hexyl)-2-methyl-3-ethylpyridinium, 1-(1 -octyl)-2-methyl-3-ethylpyridinium, 1-(1-dodecyl)-2-methyl-3-ethylpyridinium, 1-(1-tetradecyl)-2-methyl-3-ethylpyridinium, 1-(1-hexadecyl)-2-methyl-3-ethylpyridinium, 1,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium, 1-(1-butyl)-3-methylimidazolium, 1-(1-hexyl)-3-methylimidazolium, 1-(1-octyl)-3-methylimidazolium, 1-(1-dodecyl)-3-methylimidazolium, 1-(1-tetradecyl)-3-methylimidazolium, 1-(1-hexadecyl)-3-methylimidazolium, 1,2-dimethylimidazolium, 1,2,3-trimethylimidazolium, 1-ethyl-2,3-dimethylimidazolium, 1-(1-butyl)-2,3-dimethylimidazolium, 1-(1-hexyl)-2,3-dimethylimidazolium and 1-(1-octyl)-2,3-dimethylimidazolium, 1,4-dimethylimidazolium, 1,3,4-trimethylimidazolium, 1,4-dimethyl-3-ethylimidazolium, 3-butylimidazolium, 1,4-dimethyl-3-octylimidazolium, 1,4,5-trimethylimidazolium, 1,3,4,5-tetramethylimidazolium, 1,4,5-trimethyl-3-ethylimidazolium, 1,4,5-trimethyl-3-butylimidazolium, butylmethylpyrrolidinium and 1,4,5-trimethyl-3-octylimidazolium.

The metal cations [M¹]⁺, [M²]⁺, [M³]⁺, [M⁴]²⁺ and [M⁵]³⁺ mentioned in the formulae (IIIa) to (IIIj) are in general metal cations of groups 1, 2, 6, 7, 8, 9, 10, 11, 12 and 13 of the Periodic Table. Suitable metal cations are, for example, Li⁺, Na⁺, K⁺, Cs⁺, Mg²⁺, Ca²⁺, Ba²⁺, Cr³⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Ag⁺, Zn²⁺ and Al³⁺.

As anions, it is in principle possible to use all anions as long as AlCl₄ ⁻ and/or Al₂Cl₇ ⁻ are predominantly present.

The anion [Y]^(n−) of the ionic liquid is, for example, selected from

-   -   the group of halides and halogen-comprising compounds of the         formulae:

-   F⁻, Cl⁻, Br⁻, I⁻, BF₄ ⁻, PF₆ ⁻, Al₃Cl₁₀ ⁻, AlBr₄ ⁻, FeCl₄ ⁻, BCl₄ ⁻,     SbF₆ ⁻, AsF₆ ⁻, ZnCl₃ ⁻, SnCl₃ ⁻, CuCl₂ ⁻, CF₃SO₃ ⁻, (CF₃SO₃)₂N⁻,     CF₃CO₂ ⁻, CCl₃CO₂ ⁻, CN⁻, SCN⁻, OCN⁻, advantageously F⁻, Cl⁻, Br⁻,     I⁻, BF₄ ⁻, PF₆ ⁻, CF₃SO₃ and (CF₃SO₃)₂N⁻     -   the group of sulfates, sulfites and sulfonates of the general         formulae:

-   SO₄ ²⁻, HSO₄ ⁻, SO₃ ²⁻, HSO₃ ⁻, R^(a)OSO₃ ⁻, R^(a)SO₃ ⁻;     advantageously SO₄ ²⁻, SO₃ ²⁻; R^(a)OSO₃ ⁻; R^(a)SO₃ ⁻     -   the group of phosphates of the general formulae:

-   PO₄ ³⁻, HPO₄ ²⁻, H₂PO₄ ⁻, R^(a)PO₄ ²⁻, HR^(a)PO₄ ⁻, R^(a)R^(b)PO₄ ⁻;     advantageously PO₄ ³⁻; R^(a)PO₄ ²⁻, R^(a)R^(b)PO₄ ⁻     -   the group of phosphonates and phosphinates of the general         formulae:

-   R^(a)HPO₃ ⁻, R^(a)R^(b)PO₂ ⁻, R^(a)R^(b)PO₃ ⁻; advantageously     R^(a)R^(b)PO₂ ⁻; R^(a)R^(b)PO₃ ⁻     -   the group of phosphites of the general formulae:

-   PO₃ ³⁻, HPO₃ ²⁻, H₂PO₃ ⁻, R^(a)PO₃ ²⁻, R^(a)HPO₃ ⁻, R^(a)R^(b)PO₃ ⁻;     advantageously PO₃ ³⁻; R^(a)PO₃ ²⁻; R^(a)R^(b)PO₃ ⁻     -   the group of phosphonites and phosphinites of the general         formulae:

-   R^(a)R^(b)PO₂ ⁻, R^(a)HPO₂ ⁻, R^(a)R^(b)PO⁻, R^(a)HPO⁻;     advantageously R^(a)R^(b)PO₂ ⁻; R^(a)R^(b)PO⁻     -   the group of carboxylic acids of the general formula:

-   R^(a)COO⁻     -   the group of borates of the general formulae:

-   BO₃ ³⁻, HBO₃ ²⁻, H₂BO₃ ⁻, R^(a)R^(b)BO₃ ⁻, R^(a)HBO₃ ⁻, R^(a)BO₃ ²⁻,     B(OR^(a))(OR^(b))(OR^(c))(OR^(d)); B(HSO₄)⁻, B(R^(a)SO₄)⁻;     advantageously BO₃ ³⁻; R^(a)R^(b)BO₃ ⁻; R^(a)BO₃ ²⁻;     B(OR^(a))(OR^(b))(OR^(c))(OR^(d))⁻, B(R^(a)SO₄)⁻     -   the group of boronates of the general formulae:     -   R^(a)BO₂ ²⁻, R^(a)R^(b)BO⁻     -   the group of carbonates and carbonic esters of the general         formulae:

-   HCO3⁻, CO₃ ²⁻, R^(a)CO₃ ⁻; advantageously CO₃ ²⁻, R^(a)CO₃ ⁻     -   the group of silicates and silicic esters of the general         formulae:

-   SiO₄ ⁴⁻, HSiO₄ ³⁻, H₂SiO₄ ²⁻, H₃SiO₄ ⁻, R^(a)SiO₄ ³⁻, R^(a)R^(b)SiO₄     ²⁻, R^(a)R^(b)R^(c)SiO₄ ⁻, HR^(a)SiO₄ ²⁻, H₂R^(a)SiO₄ ⁻,     HR^(a)R^(b)SiO₄ ⁻, advantageously SiO₄ ⁴⁻, R^(a)SiO₄ ³⁻,     R^(a)R^(b)SiO₄ ²⁻, R^(a)R^(b)R^(c)SiO₄ ⁻     -   the group of alkylsilane and arylsilane salts of the general         formulae:

-   R^(a)SiO₃ ³⁻, R^(a)R^(b)SiO₂ ²⁻, R^(a)R^(b)R^(c)SiO⁻,     R^(a)R^(b)R^(c)SiO₂ ⁻, R^(a)R^(b)SiO₃ ²⁻     -   the group of carboximides, bis(sulfonyl)imides and         sulfonylimides of the general formulae:

-   -   the group of methides of the general formula:

-   -   the group of alkoxides and aryloxides of the general formula:         -   R^(a)O⁻;     -   the group of halometalates of the general formula:

[M_(q)Hal_(r)]^(s−),

-   -   -   where M is a metal and Hal is fluorine, chlorine, bromine or             iodine, q and r are positive integers and indicate the             stoichiometry of the complex and s is a positive integer and             indicates the charge on the complex;

    -   the group of sulfides, hydrogensulfides, polysulfides,         hydrogenpolysulfides and thiolates of the general formulae:

S²⁻, HS⁻, [S_(v)]²⁻, [HS_(v)]⁻, [R^(a)S]⁻,

-   -   -   where v is a positive integer from 2 to 10; advantageously             S²⁻, [S_(v)]²⁻, [R^(a)S]⁻

    -   the group of complex metal ions such as Fe(CN)₆ ³⁻, Fe(CN)₆ ⁴⁻,         MnO₄ ⁻, Fe(CO)₄ ⁻.

Here, R^(a), R^(b), R^(c) and R^(d) are each, independently of one another, hydrogen, C₁-C₃₀-alkyl, C₂-C₁₈-alkyl which is optionally interrupted by one or more nonadjacent oxygen and/or sulfur atoms and/or one or more substituted or unsubstituted imino groups, C₆-C₁₄-aryl, C₅-C₁₂-cycloalkyl or a five- or six-membered, oxygen-, nitrogen- and/or sulfur-comprising heterocycle, where two of the radicals may together form an unsaturated, saturated or aromatic ring which is optionally interrupted by one or more oxygen and/or sulfur atoms and/or one or more unsubstituted or substituted imino groups, where the radicals mentioned may in each case also be substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles. R^(a), R^(b), R^(c) and R^(d) are advantageously different from hydrogen.

Here, C₁-C₁₈-alkyl which is optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles is, for example, methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, 2,4,4-trimethylpentyl, decyl, dodecyl, tetradecyl, heptadecyl, octadecyl, 1,1-dimethylpropyl, 1,1-dimethylbutyl, 1,1,3,3-tetramethylbutyl, benzyl, 1-phenylethyl, α,α-dimethylbenzyl, benzhydryl, p-tolylmethyl, 1-(p-butylphenyl)ethyl, p-chlorobenzyl, 2,4-dichlorobenzyl, p-methoxybenzyl, m-ethoxybenzyl, 2-cyanoethyl, 2-cyanopropyl, 2-methoxycarbonethyl, 2-ethoxycarbonylethyl, 2-butoxycarbonylpropyl, 1,2-di(methoxycarbonyl)ethyl, 2-methoxyethyl, 2-ethoxyethyl, 2-butoxyethyl, diethoxy-methyl, diethoxyethyl, 1,3-dioxolan-2-yl, 1,3-dioxan-2-yl, 2-methyl-1,3-dioxolan-2-yl, 4-methyl-1,3-dioxolan-2-yl, 2-isopropoxyethyl, 2-butoxypropyl, 2-octyloxyethyl, chloromethyl, trichloromethyl, trifluoromethyl, 1,1-dimethyl-2-chloroethyl, 2-methoxy-isopropyl, 2-ethoxyethyl, butylthiomethyl, 2-dodecylthioethyl, 2-phenlythioethyl, 2,2,2-trifluoroethyl, 2-dimethylaminoethyl, 2-dimethylaminopropyl, 3-dimethylaminopropyl, 4-dimethylaminobutyl, 6-dimethylaminohexyl, 2-phenoxyethyl, 2-phenoxypropyl, 3-phenoxypropyl, 4-phenoxybutyl, 6-phenoxyhexyl, 2-methoxyethyl, 2-methoxypropyl, 3-methoxypropyl, 4-methoxybutyl, 6-methoxyhexyl, 2-ethoxyethyl, 2-ethoxypropyl, 3-ethoxypropyl, 4-ethoxybutyl or 6-ethoxyhexyl.

C₂-C₁₈-Alkyl which is optionally interrupted by one or more nonadjacent oxygen and/or sulfur atoms and/or one or more substituted or unsubstituted imino groups is, for example, 5-hydroxy-3-oxapentyl, 8-hydroxy-3,6-dioxaoctyl, 11-hydroxy-3,6,9-trioxaundecyl, 7-hydroxy-4-oxaheptyl, 11-hydroxy-4,8-dioxaundecyl, 15-hydroxy-4,8,12-trioxapentadecyl, 9-hydroxy-5-oxanonyl, 14-hydroxy-5,10-oxatetradecyl, 5-methoxy-3-oxapentyl, 8-methoxy-3,6-dioxaoctyl, 11-methoxy-3,6,9-trioxaundecyl, 7-methoxy-4-oxaheptyl, 11-methoxy-4,8-dioxaundecyl, 15-methoxy-4,8,12-trioxapenta-decyl, 9-methoxy-5-oxanonyl, 14-methoxy-5,10-oxatetradecyl, 5-ethoxy-3-oxapentyl, 8-ethoxy-3,6-dioxaoctyl, 11-ethoxy-3,6,9-trioxaundecyl, 7-ethoxy-4-oxaheptyl, 11-ethoxy-4,8-dioxaundecyl, 15-ethoxy-4,8,12-trioxapentadecyl, 9-ethoxy-5-oxanonyl or 14-ethoxy-5,10-oxatetradecyl.

If two radicals form a ring, these radicals together can be, for example as fused-on building block, 1,3-propylene, 1,4-butylene, 2-oxa-1,3-propylene, 1-oxa-1,3-propylene, 2-oxa-1,3-propenylene, 1-aza-1,3-propenylene, 1-C₁-C₄-alkyl-1-aza-1,3-propenylene, 1,4-buta-1,3-dienylene, 1-aza-1,4-buta-1,3-dienylene or 2-aza-1,4-buta-1,3-dienylene.

The number of nonadjacent oxygen and/or sulfur atoms and/or imino groups is not restricted in principle or is restricted automatically by the size of the radical or the ring building block. In general, there will be no more than 5 in the respective radical, preferably no more than 4 and very particularly preferably no more than 3. Furthermore, there is generally at least one carbon atom, preferably at least two carbon atoms, between each two heteroatoms.

Substituted and unsubstituted imino groups can be, for example, imino, methylimino, isopropylimino, n-butylimino or tert-butylimino.

The term “functional groups” refers, for example, to the following: carboxy, di(C₁-C₄-alkyl)amino, C₁-C₄-alkyloxycarbonyl, cyano or C₁-C₄-alkoxy. Here, C₁-C₄-alkyl is methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl or tert-butyl.

C₆-C₁₄-Aryl which is optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles is, for example, phenyl, tolyl, xylyl, α-naphthyl, β-naphthyl, 4-diphenylyl, chlorophenyl, dichlorophenyl, trichlorophenyl, difluorophenyl, methylphenyl, dimethylphenyl, trimethylphenyl, ethylphenyl, diethylphenyl, isopropylphenyl, tert-butylphenyl, dodecylphenyl, methoxyphenyl, dimethoxyphenyl, ethoxyphenyl, hexyloxyphenyl, methylnaphthyl, isopropylnaphthyl, chloronaphthyl, ethoxynaphthyl, 2,6-dimethylphenyl, 2,4,6-trimethylphenyl, 2,6-dimethoxyphenyl, 2,6-dichlorophenyl, 4-bromophenyl, 2- or 4-nitrophenyl, 2,4- or 2,6-dinitrophenyl, 4-dimethylaminophenyl, 4-acetylphenyl, methoxyethylphenyl or ethoxymethylphenyl.

C₅-C₁₂-Cycloalkyl which is optionally substituted by functional groups, aryl, alkyl, aryloxy, halogen, heteroatoms and/or heterocycles is, for example, cyclopentyl, cyclohexyl, cyclooctyl, cyclododecyl, methylcyclopentyl, dimethylcyclopentyl, methylcyclohexyl, dimethylcyclohexyl, diethylcyclohexyl, butylcyclohexyl, methoxycyclohexyl, dimethoxycyclohexyl, diethoxycyclohexyl, butylthiocyclohexyl, chlorocyclohexyl, dichlorocyclohexyl, dichlorocyclopentyl or a saturated or unsaturated bicyclic system such as norbornyl or norbornenyl.

A five- or six-membered, oxygen-, nitrogen- and/or sulfur-comprising heterocycle is, for example, furyl, thiophenyl, pyryl, pyridyl, indolyl, benzoxazolyl, dioxolyl, dioxyl, benzimidazolyl, benzthiazolyl, dimethylpyridyl, methylquinolyl, dimethylpyryl, methoxyfuryl, dimethoxypyridyl, difluoropyridyl, methylthiophenyl, isopropylthiophenyl or tert-butylthiophenyl.

Preferred anions are selected from the group of halides and halogen-comprising compounds, the group of carboxylic acids, the group of sulfates, sulfites and sulfonates and the group of phosphates.

Preferred anions are chloride, bromide, iodide, SCN⁻, OCN⁻, CN⁻, acetate, C₁-C₄-alkylsulfates, R^(a)—COO⁻, R^(a)SO₃ ⁻, R^(a)R^(b)PO₄ ⁻, methanesulfonates, tosylate, C₁-C₄-dialkylphosphates, hydrogensulfate or tetrachloroaluminate.

Particular preference is given to using dialkylimidazolium cations in which the two alkyl groups can be identical or different, branched or unbranched, unsubstituted or substituted by one or more phenyl groups and have from 1 to 6 carbon atoms.

Very particular preference is given to benzylmethylimidazolium, hexylmethylimidazolium, butylmethylimidazolium, ethylmethylimidazolium.

As anions, very particular preference is given to tetrachloroaluminate and/or heptachlorodialuminate and/or F⁻ and/or Cl⁻ and/or Br⁻ and/or BF₄ ⁻ and/or PF₆ ⁻ and/or CF₃SO₃ ⁻ and/or (CF₃SO₃)₂N⁻ and/or SO₄ ²⁻ and/or SO₃ ²⁻ and/or PO₄ ³⁻.

In the step (a) of the process of the invention for the electrochemical deposition of aluminum, an electrolysis apparatus which has at least one anode and at least one cathode in an electrolysis space is provided. Here, the at least one anode and the at least one cathode are connected in an electrolytically conductive fashion by the electrolyte, which is an ionic liquid.

It is possible to use one anode, but a plurality of anodes can also be employed. These can have the same composition or different compositions. The same applies to the cathode(s).

In an embodiment of the invention, the anode functions as sacrificial anode comprising primary aluminum.

The at least one anode preferably comprises aluminum in a proportion by weight of at least 95% by weight, preferably 99% by weight, more preferably at least 99.5% by weight, based on the total weight of the at least one anode.

The composition of the cathode can be selected in a known manner.

The at least one cathode present in the electrolysis apparatus can be selected from among various conductive materials. In a general embodiment of the invention, the at least one cathode comprises a material or a plurality of materials selected from among metals, alloys, graphite, electrically conductive plastics or polymers and steels. In a preferred embodiment, the material of the cathode is selected from among metals, alloys and steels, in particular from among steel, Ni alloys, Cu alloys, Zn alloys and Al alloys.

Deposition onto graphite felts, woven metal fabrics, woven fiberglass fabrics and graphite fabrics is also possible, so that composites can be obtained directly.

Preference is given to using a three-dimensional cathode. Further preferred examples of suitable cathode materials are stainless steel, nickel-based alloys, graphite, copper and particularly preferably aluminum.

Advantageously the electrolyte is agitated at the surface of the cathode, e.g. by means of stirring, recirculation or agitation of the whole apparatus.

The shapes of the anode and of the cathode can in principle be selected freely. Preference is given to selecting arrangements known in the prior art. In a preferred embodiment of the invention, the cathode is a workpiece such as a vehicle bodywork part on which aluminum is deposited.

Suitable arrangements are described in chapter 5 of T. W. Jelinek, Praktische Galvanotechnik, 2005 (ISBN 3-87 480-207-8).

In a general embodiment of the invention, the process of the invention is carried out at a temperature in the range from 20 to 200° C., preferably at a temperature in the range from 20 to 120° C., particularly preferably at a temperature in the range from 60 to 90° C., very particularly preferably at a temperature of about 90° C.

The aluminum is generally supplied to the process of the invention in the form of a metal salt selected from the group consisting of AlCl₃, AlBr₃, AlI₃ and AlF₃. Preference is given to AlCl₃

The invention further provides for the use of additives having the general formulae (I), (II) and (III) in a process for the electrochemical deposition of aluminum.

The invention further provides an electrolyte for the electrochemical deposition of aluminum from an ionic liquid comprising an ionic liquid comprising anions and cations and also one or more metal salts, one or more additives of the general formulae (I), (II) and (III) and also, if appropriate, one or more solvents.

The electrolyte of the invention in combination with one or more additives of the general formulae (I), (II) and (III) is found to be very progressive from an electroplating point of view, i.e. it fulfills the requirements which an electrolyte has to meet for an industrially widely usable and economical aluminum deposition process to a far higher extent than has hitherto been possible. A further advantage of the electrolyte of the invention is that when it is used in the electrochemical deposition of aluminum, it leads to an even deposit of aluminum having a shiny or matt finish on the cathode.

The composition of the electrolyte of the invention can generally vary over a wide range; thus, the electrolyte of the invention comprises from 0.1 to 10% by weight of additive and from 99.9 to 90% by weight of ionic liquid and from 0 to 50% by weight, preferably from 10 to 30% by weight, of one or more organic solvent(s). The organic solvent is generally selected from the group consisting of aromatics and heteroaromatics. In a preferred embodiment of the invention, the solvent is selected from among toluene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,3-dichlorobenzene, trichlorobenzene and xylene.

The present invention is illustrated by the following examples.

EXAMPLE 1 Deposition of Aluminum from EMIMCI×1.5 AlCl₃ in the Presence of 5% by Weight of N-Methylbenzotriazole

95 g of EMIMCI×1.5 AlCl₃ are placed in a heatable/coolable double-walled electrolysis cell and slowly admixed with 5 g of N-methylbenzotriazole. The reaction mixture is heated to 95° C. under a protective argon atmosphere, forming a homogeneous solution from the initial suspension. An Al anode and an Al cathode (both degreased) having an electrode spacing of 2 cm and an active surface area of in each case 5 cm² (1×5 cm) are introduced into the electrolysis cell. An anodic pulse having a potential of 1 V is applied to the cathode over a period of 10 sec. The polarity is then reversed again and aluminum is deposited on the cathode over a further 286 minutes at 95° C. and a current density of 40 mA/cm², with the anode simultaneously being consumed as a sacrificial anode. During the course of the experiment, the terminal voltage drops from 991 to 801 mV. After the electrolysis is complete, the electrodes are removed from the electrolyte and successively rinsed with 40 ml of acetonitrile, stirred in 100 ml of water for 15 minutes and rinsed with isopropanol. They are finally dried at 105° C. for one hour. From the cathodic mass difference, the current yield is determined as 97.3%. The appearance of the cathode deposit is matt and dense.

EXAMPLE 2 Deposition of Aluminum from EMIMCI×1.5 AlCl₃ in the presence of 1% by Weight of Benzothiazole

99 g of EMIMCI×1.5 AlCl₃ are placed in a heatable/coolable double-walled electrolysis cell, slowly admixed with 1 g of benzothiazole and heated to 95° C. under a protective argon atmosphere. An Al anode and an Al cathode (both degreased) having an electrode spacing of 2 cm and an active surface area of in each case 5 cm² (1×5 cm) are introduced into the electrolysis cell. An anodic pulse having a potential of 1 V is applied to the cathode over a period of 10 sec. The polarity is then reversed again and aluminum is deposited on the cathode over a further 286 minutes at 95° C. and a current density of 40 mA/cm², with the anode simultaneously being consumed as a sacrificial anode. During the course of the experiment, the terminal voltage drops from 974 to 850 mV. After the electrolysis is complete, the electrodes are removed from the electrolyte and successively rinsed with 40 ml of acetonitrile, stirred in 100 ml of water for 15 minutes and rinsed with isopropanol. They are finally dried at 105° C. for one hour. From the cathodic mass difference, the current yield is determined as 95.8%. The appearance of the gray cathode deposit is matt and dense.

EXAMPLE 3 Deposition of Aluminum from EMIMCI×1.5 AlCl₃ in the Presence of 10% by Weight of Hexadecyltrimethylammonium Chloride

90 g of EMIMCI×1.5 AlCl₃ are placed in a heatable/coolable double-walled electrolysis cell and slowly admixed with 10 g of hexadecyltrimethylammonium chloride. The reaction mixture is heated to 95° C. under a protective argon atmosphere, forming a homogeneous solution from the initial suspension. An Al anode and an Al cathode (both degreased) having an electrode spacing of 2 cm and an active surface area of in each case 5 cm² (1×5 cm) are introduced into the electrolysis cell. An anodic pulse having a potential of 1 V is applied to the cathode over a period of 10 sec. The polarity is then reversed again and aluminum is deposited on the cathode over a further 141 minutes at 95° C. and a current density of 80 mA/cm², with the anode simultaneously being consumed as a sacrificial anode. During the course of the experiment, the terminal voltage drops from 1812 mV to 1626 mV. After the electrolysis is complete, the electrodes are removed from the electrolyte and successively rinsed with 40 ml of acetonitrile, stirred in 100 ml of water for 15 minutes and rinsed with isopropanol. They are finally dried at 105° C. for one hour. From the cathodic mass difference, the current yield is determined as 91.3%. The appearance of the cathode deposit is shiny and silvery.

EXAMPLE 4 Deposition of Aluminum from EMIMCI×1.5 AlCl₃ in the Presence of 9% by Weight of Hexadecyltrimethylammonium Chloride

91 g of EMIMCI×1.5 AlCl₃ are placed in a heatable/coolable double-walled electrolysis cell and slowly admixed with 9 g of hexadecyltrimethylammonium chloride. The reaction mixture is heated to 95° C. under a protective argon atmosphere, forming a homogeneous solution from the initial suspension. An Al anode and an Al cathode (both degreased) having an electrode spacing of 2 cm and an active surface area of in each case 5 cm² (1×5 cm) are introduced into the electrolysis cell. An anodic pulse having a potential of 1 V is applied to the cathode over a period of 10 sec. The polarity is then reversed again and aluminum is deposited on the cathode over a further 266 minutes at 95° C. and a current density of 40 mA/cm², with the anode simultaneously being consumed as a sacrificial anode. During the course of the experiment, the terminal voltage drops from 1296 mV to 805 mV. After the electrolysis is complete, the electrodes are removed from the electrolyte and successively rinsed with 40 ml of acetonitrile, stirred in 100 ml of water for 15 minutes and rinsed with isopropanol. They are finally dried at 105° C. for one hour. From the cathodic mass difference, the current yield is determined as 100%. The appearance of the gray cathode deposit is matt and dense.

EXAMPLE 5 Deposition of Aluminum from EMIMCI×1.5 AlCl₃ in the Presence of 1% by Weight of Na Laurylsulfate

99 g of EMIMCI×1.5 AlCl₃ are placed in a heatable/coolable double-walled electrolysis cell and slowly admixed with 1 g of Na laurylsulfate. The reaction mixture is heated to 95° C. under a protective argon atmosphere, forming a homogeneous solution from the initial suspension. An Al anode and an Al cathode (both degreased) having an electrode spacing of 2 cm and an active surface area of in each case 5 cm² (1×5 cm) are introduced into the electrolysis cell. An anodic pulse having a potential of 1 V is applied to the cathode over a period of 10 sec. The polarity is then reversed again and aluminum is deposited on the cathode over a further 140 minutes at 95° C. and a current density of 80 mA/cm², with the anode simultaneously being consumed as a sacrificial anode. During the course of the experiment, the terminal voltage drops from 1875 mV to 1569 mV. After the electrolysis is complete, the electrodes are removed from the electrolyte and successively rinsed with 40 ml of acetonitrile, stirred in 100 ml of water for 15 minutes and rinsed with isopropanol. They are finally dried at 105° C. for one hour. From the cathodic mass difference, the current yield is determined as 93.1%. The appearance of the cathode deposit is shiny and dense.

EXAMPLE 6 Deposition of Aluminum from 80.9% by Weight of EMIMCI×1.5 AlCl₃+9.1% by Weight of Hexadecyltrimethylammonium Chloride+10% by Weight of Toluene

59.8 g of EMIMCI×1.5 AlCl₃ are placed in a heatable/coolable double-walled electrolysis cell and slowly admixed with 6.7 g of hexadecyltrimethylammonium chloride and 7.4 g of toluene at 80° C. The reaction mixture is heated to 90° C. under a protective argon atmosphere, forming a homogeneous solution. An Al anode and a Cu cathode having an electrode spacing of 1 cm and an active surface area of in each case 10 cm² (2×5 cm) are introduced into the electrolysis cell. The Cu cathode was degreased beforehand at 60° C. in 5% strength by weight Mucasol solution in an ultrasonic bath for 10 minutes, rinsed with acetone, pickled in concentrated nitric acid for 5 seconds and again rinsed with acetone. Aluminum is deposited on the cathode over a period of 1 hour at 90° C. and a current density of 40 mA/cm², with the anode simultaneously being consumed as a sacrificial anode. During the course of the experiment, the terminal voltage drops from 3.0 to 2.7 V. After the electrolysis is complete, the electrodes are removed from the electrolyte and washed with 50 ml of acetonitrile. The appearance of the cathode deposit is shiny and dense.

EXAMPLE 7 Deposition of Aluminum from 89.1% by Weight of EMIMCI×1.5 AlCl₃+0.9% by Weight of SDS (Sodium Laurylsulfate)+10% by Weight of Toluene

62.6 g of EMIMCI×1.5 AlCl₃ are placed in a heatable/coolable double-walled electrolysis cell and slowly admixed with 0.63 g of sodium laurylsulfate and 7.0 g of toluene at 80° C. The reaction mixture is heated to 90° C. under a protective argon atmosphere, forming a homogeneous solution. An Al anode and a Cu cathode having an electrode spacing of 1 cm and an active surface area of in each case 10 cm² (2×5 cm) are introduced into the electrolysis cell. The Cu cathode was degreased beforehand at 60° C. in 5% strength by weight Mucasol solution in an ultrasonic bath for 10 minutes, rinsed with acetone, pickled in concentrated nitric acid for 5 seconds and again rinsed with acetone. Aluminum is deposited on the cathode over a period of 1 hour at 90° C. and a current density of 40 mA/cm², with the anode simultaneously being consumed as a sacrificial anode. During the course of the experiment, the terminal voltage drops from 2.2 to 1.3 V. After the electrolysis is complete, the electrodes are removed from the electrolyte and washed with 50 ml of acetonitrile. The appearance of the cathode deposit is matt and dense.

EXAMPLE 8 Deposition of Aluminum from 69.3% by Weight of EMIMCI×1.5 AlCl₃+0.7% by Weight of SDS (Sodium Laurylsulfate)+30% by Weight of Toluene

56.5 g of EMIMCI×1.5 AlCl₃ are placed in a heatable/coolable double-walled electrolysis cell and slowly admixed with 0.57 g of sodium laurylsulfate and 24.6 g of toluene at 80° C. The reaction mixture is heated to 90° C. under a protective argon atmosphere, forming a homogeneous solution. An Al anode and a Cu cathode having an electrode spacing of 1 cm and an active surface area of in each case 10 cm² (2×5 cm) are introduced into the electrolysis cell. The Cu cathode was degreased beforehand at 60° C. in 5% strength by weight Mucasol solution in an ultrasonic bath for 10 minutes, rinsed with acetone, pickled in concentrated nitric acid for 5 seconds and again rinsed with acetone. Aluminum is deposited on the cathode over a period of 1 hour at 90° C. and a current density of 40 mA/cm², with the anode simultaneously being consumed as a sacrificial anode. During the course of the experiment, the terminal voltage drops from 1.5 to 1.0 V. After the electrolysis is complete, the electrodes are removed from the electrolyte and washed with 50 ml of acetonitrile. The appearance of the cathode deposit is matt and dense.

EXAMPLE 9 Deposition of Aluminum from 69.3% by Weight of EMIMCI×1.5 AlCl₃+0.7% by Weight of SDS (Sodium Laurylsulfate)+30% by Weight of Chlorobenzene

55.4 g of EMIMCI×1.5 AlCl₃ are placed in a heatable/coolable double-walled electrolysis cell and slowly admixed with 0.56 g of sodium laurylsulfate and 24.0 g of chlorobenzene at 80° C. The reaction mixture is heated to 90° C. under a protective argon atmosphere, forming a homogeneous solution. An Al anode and a Cu cathode having an electrode spacing of 1 cm and an active surface area of in each case 10 cm² (2×5 cm) are introduced into the electrolysis cell. The Cu cathode was degreased beforehand at 60° C. in 5% strength by weight Mucasol solution in an ultrasonic bath for 10 minutes, rinsed with acetone, pickled in concentrated nitric acid for 5 seconds and again rinsed with acetone. Aluminum is deposited on the cathode over a period of 1 hour at 90° C. and a current density of 40 mA/cm², with the anode simultaneously being consumed as a sacrificial anode. During the course of the experiment, the terminal voltage remains stable at 1.2 V. After the electrolysis is complete, the electrodes are removed from the electrolyte and washed with 50 ml of acetonitrile. The appearance of the cathode deposit is silvery and dense.

EXAMPLE 10 Deposition of Aluminum from 69.3% by Weight of EMIMCI×1.5 AlCl₃+0.7% by weight of SDS (Sodium Laurylsulfate)+30% by Weight of Chlorobenzene

54.6 g of EMIMCI×1.5 AlCl₃ are placed in a heatable/coolable double-walled electrolysis cell and slowly admixed with 0.55 g of sodium laurylsulfate and 23.6 g of chlorobenzene at 80° C. The reaction mixture is heated to 90° C. under a protective argon atmosphere, forming a homogeneous solution. An Al anode and an Ni cathode having an electrode spacing of 1 cm and an active surface area of in each case 10 cm² (2×5 cm) are introduced into the electrolysis cell. The Ni cathode was degreased beforehand at 60° C. in 5% strength by weight Mucasol solution in an ultrasonic bath for 10 minutes and rinsed with acetone. Aluminum is deposited on the cathode over a period of 15 minutes at 90° C. and a current density of 40 mA/cm², with the anode simultaneously being consumed as a sacrificial anode. During the course of the experiment, the terminal voltage increases from 1.2 to 1.3 V. After the electrolysis is complete, the electrodes are removed from the electrolyte and washed with 50 ml of acetonitrile. The appearance of the cathode deposit is silvery-matt and dense.

EXAMPLE 11 Deposition of Aluminum from 69.3% by Weight of EMIMCI×1.5 AlCl₃+0.7% by Weight of SDS (Sodium Laurylsulfate)+30% by Weight of Chlorobenzene

67.7 g of EMIMCI×1.5 AlCl₃ are placed in a heatable/coolable double-walled electrolysis cell and slowly admixed with 0.68 g of sodium laurylsulfate and 29.3 g of chlorobenzene at 80° C. The reaction mixture is heated to 90° C. under a protective argon atmosphere, forming a homogeneous solution. An Al anode and a mild steel cathode having an electrode spacing of 1 cm and an active surface area of in each case 10 cm² (2×5 cm) are introduced into the electrolysis cell. The mild steel cathode was electrolytically degreased beforehand by means of the Metex Cleaner System from MacDermid, rinsed with water, pickled with concentrated hydrochloric acid for 10 seconds and rinsed with acetone. Aluminum is deposited on the cathode over a period of 15 minutes at 90° C. and a current density of 40 mA/cm², with the anode simultaneously being consumed as a sacrificial anode. During the course of the experiment, the terminal voltage increases from 1.3 to 1.5 V. After the electrolysis is complete, the electrodes are removed from the electrolyte and washed with 50 ml of acetonitrile. The appearance of the cathode deposit is silvery and dense. 

1. A process for the electrochemical deposition of aluminum, comprising electrochemically depositing aluminum on at least one cathode of an electrolysis apparatus comprising the at least one cathode and at least one anode and from an ionic liquid, wherein: current density at the at least one cathode is at least 50 A/m², the ionic liquid comprises anions and cations, at least one metal salt, and at least one additive, the amount of the at least one additive is from 0.1 to 10% by weight, based on the total amount of the ionic liquid, and the at least one additive is selected from the group consisting of: (a) a compound of the general formula (I):

wherein: X¹ and X² are each, independently of one another, N or CH, X³ is selected from the group consisting of NR¹, O and S, m is an integer from 0 to 4, at least two of X¹, X² and X³ are heteroatoms selected from the group consisting of N, O and S, R¹ is selected from the group consisting of H, alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl and heterocyclyl, where the alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl and heterocyclyl groups are optionally substituted by one or more substituents and the alkyl and cycloalkyl groups are optionally interrupted by from 1 to 3 heteroatoms or functional groups, and the radicals R² are each, independently of one another, H, alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl or heterocyclyl, where the alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl and heterocyclyl groups are optionally substituted by one or more substituents and the alkyl and cycloalkyl groups are optionally interrupted by from 1 to 3 heteroatoms or functional groups, (b) a compound of the general formula (I): R³N⁺(R⁴)₃HAI⁻  (II) wherein: R³ is H, alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl or heterocyclyl, where the alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl and heterocyclyl groups are optionally substituted by one or more substituents and the alkyl and cycloalkyl groups are optionally interrupted by from 1 to 3 heteroatoms or functional groups, and the radicals R⁴ are each, independently of one another, H, alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl or heterocyclyl, where the alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl and heterocyclyl groups are optionally substituted by one or more substituents and the alkyl and cycloalkyl groups are optionally interrupted by from 1 to 3 heteroatoms or functional groups, and Hal is selected from the group consisting of fluorine, chlorine, bromine and iodine, and (c) a compound of the general formula (III): R⁵SO₃ ⁻M⁺  (III) wherein: R5 is alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl or heterocyclyl, where the alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl and heterocyclyl groups are optionally substituted by one or more substituents and the alkyl and cycloalkyl groups are optionally interrupted by from 1 to 3 heteroatoms or by functional groups, and M⁺ is Na⁺ or K⁺.
 2. The process of claim 1, wherein the compound of the general formula (I) is selected from the group consisting of N-methylbenzothiazole, N-ethylbenzodiazole, benzooxazole, benzisooxazole, benzisothiazole and benzothiazole.
 3. The process of claim 1, wherein the compound of the general formula (II) is selected from the group consisting of hexadecyltrimethylammonium bromide and hexadecyltrimethylammonium chloride.
 4. The process of claim 1, wherein the compound of the general formula (III) is sodium laurylsulfate.
 5. The process of claim 1, wherein the cations of the ionic liquid comprise at least one cation selected from the group consisting of pyridinium, pyrrolidinium, pyrazolinium, pyrazolium, imidazolium and ammonium.
 6. The process of claim 1, wherein the anions of the ionic liquid comprise at least one anion selection from the group consisting of tetrachloroaluminate and heptachlorodialuminate.
 7. The process of claim 1, wherein the process is carried out at a temperature in the range from 20 to 120° C.
 8. The process of claim 1, wherein a current density of from 200 to 2000 A/m² is applied between the at least one anode and the at least one cathode.
 9. The process of claim 1, wherein the at least one metal salt is selected from the group consisting of AlCl₃, AlBr₃, AlI₃ and AlF₃.
 10. The process of claim 1, wherein the at least one anode comprises a material selected from the group consisting of steel, stainless steel, nickel-based alloys, graphite, copper and aluminum.
 11. An electrolyte for the electrochemical deposition of aluminum comprising an ionic liquid comprising anions and cations, at least one metal salt, and at least one additive, wherein: the at least one additive is selected from the group consisting of: (a) a compound of the general formula (I):

wherein: X¹ and X² are each, independently of one another, N or CH, X³ is NR¹, O or S, m is an integer from 0 to 4, at least two of X¹, X² and X³ are heteroatoms selected from the group consisting of N, O and S, R¹ is selected from the group consisting of H, alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl and heterocyclyl, where the alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl and heterocyclyl groups are optionally substituted by one or more substituents and the alkyl and cycloalkyl groups are optionally interrupted by from 1 to 3 heteroatoms or functional groups, and the radicals R² are each, independently of one another, H, alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl or heterocyclyl, where the alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl and heterocyclyl groups are optionally substituted by one or more substituents or are interrupted by from 1 to 3 heteroatoms or functional groups, (b) a compound of the general formula (II): R³N⁺(R⁴)₃HAI⁻  (II) wherein: R³ is H, alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl or heterocyclyl, where the alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl and heterocyclyl groups are optionally substituted by one or more substituents and the alkyl and cycloalkyl groups are optionally interrupted by from 1 to 3 heteroatoms or functional 20 groups, and the radicals R⁴ are each, independently of one another, H, alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl or heterocyclyl, where the alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl and heterocyclyl groups are optionally substituted by one or more 25 substituents or are interrupted by from 1 to 3 heteroatoms or functional groups, and Hal is selected from the group consisting of fluorine, chlorine, bromine and iodine, and (c) a compound of the general formula (III): R⁵SO₃ ⁻M⁺  (III) wherein: R5 is alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl or heterocyclyl, where the alkyl, cycloalkyl, aralkyl, aryl, alkoxyaryl and heterocyclyl groups are optionally substituted by one or more substituents and the alkyl and cycloalkyl groups are optionally interrupted by from 1 to 3 heteroatoms or by functional groups, and M⁺ is Na⁺ or K⁺.
 12. The electrolyte of claim 11, wherein the at least one metal salt comprises AlCl₃.
 13. (canceled)
 14. A process for electrochemical deposition of aluminum, the process comprising electrochemically depositing aluminum onto at least one cathode from the electrolyte of claim
 11. 15. The process of claim 1, wherein the at least one cathode comprises a material selection from the group consisting of steel, stainless steel, nickel-based alloys, graphite, copper and aluminum.
 16. The process of claim 1, wherein the at least one cathode and the at least one anode comprise a material selection from the group consisting of steel, stainless steel, nickel-based alloys, graphite, copper and aluminum.
 17. The electrolyte of claim 11, further comprising at least one solvent.
 18. The electrolyte of claim 17, wherein the at least one solvent is selected from the group consisting of toluene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,3-dichlorobenzene, trichlorobenzene and xylene. 